1. Field of the Invention
The invention relates to a light source device using a HID lamp which is used for example as a light source for a projector.
2. Description of the Related Art
In an optical device, such as a liquid crystal projector, a DLP(copyright) projector (manufactured by Texas Instruments), a discharge lamp with high radiance lamp (HID), such as a high pressure mercury lamp, a xenon lamp, a metal halide lamp or the like is used. In one such discharge lamp, it is necessary to produce a high voltage using a starter device which will expose the discharge space to an insulation breakdown in order to start a discharge.
FIG. 14 shows the arrangement of a conventional discharge lamp light source device of the series trigger type. In a light source device for an optical device normally a starter (Ui) is used in which a pulsed high voltage is applied between the electrodes (E1, E2) of the two poles of the discharge lamp. In this system, the secondary winding (Si) of the high voltage transformer (Ti) of the starter is series-connected to the discharge lamp (Li). After starting a discharge the function of the starter is no longer necessary. The discharge current supplied to the lamp (Li) must nonetheless flow via the secondary winding (Si) of the high voltage transformer, which has a large number of windings. In order to reduce the loss of heat in the winding (Si), it is necessary to make the wire diameter of the winding large, which inevitably results in the disadvantage of an increase in size and weight of the starter.
One method for avoiding this disadvantage has been to use an outside trigger method which is often used for the trigger of a blinking lamp. In this method, in addition to the first electrode and the second electrode of the two poles which form the main arc discharge after starting, there is provided an auxiliary electrode, positioned between either the first or the second electrode to which a high voltage is applied. This results in dielectric barrier discharge plasma being produced in the discharge space, which then creates the main arc discharge between the first electrode and the second electrode by means of a voltage which has been applied beforehand, i.e., a no-load voltage, by means of a plasma.
In this arrangement, after starting the discharge of the lamp no discharge current the lamp flows through the primary winding and the secondary winding of the high voltage transformer of the starter. Therefore, the primary winding and secondary winding of the high voltage transformer of the starter suffers no heat loss. This method avoids an increase in both the size and weight of the starter.
On the other hand, with regard to the conventional discharge lamp (Li), the discharge lamp (Li) and the feed device (Ni) are connected to one another by feed lines (K1, K2). Additionally, the starter (Ui) unit is located inside the feed device (Ni). This starter (Ui) must produce a high voltage, e.g., a high pulsed voltage, so that the feed lines (K1, K2) are charged in a short time with a high voltage which results in the disadvantage of creating a powerful noise in the lines.
Furthermore, a dulling distortion of the pulsed high voltage is created by an electrostatic buildup which is formed between the feed lines (K1, K2) and any lead in the vicinity, and as well as an inductance of the feed lines (K1, K2). As a result, the buildup of voltage between the lamp electrodes (E1, E2) is therefore reduced. In order to obtain the pulsed voltage necessary for starting the discharge lamp, a larger amount of energy than is normally necessary must be delivered by the starter (Ui) in the direction to the feed lines (K1, K2). In addition, the pulse width is broadened by dulling distortion of the pulsed high voltage which increases the possibility of the formation of an insulation breakdown in an unintended area, such as in the insulation coating of the high voltage transformer (Ti) and the feed lines (K1, K2) or the like. This reduces the reliability of the discharge lamp.
In another method of starting a discharge lamp, a starter, referred to as a DC starter, produces a high voltage where the voltage increases relatively slowly. However, in this instance the insulation breakdown phenomenon is more frequent, as well as resulting in a higher voltage and a longer voltage application time. The disadvantage in this method is an even greater possibility exists for the formation of an insulation breakdown in an unintended area.
As was described above with regard to the outside trigger method, the disadvantage of formation of an insulation breakdown in an unintended area, when using a DC starter, is exactly the same as the series trigger method. For example, Japanese patent publication JP 37-8045 discloses a discharge lamp in which the technique for starting the high pressure discharge lamp is by the outside trigger method. In this arrangement, there is a coil which produces, at the lamp current in the high pressure mercury lamp, a magnetic force. The operation of the starter circuit is controlled so that a high voltage is produced in an auxiliary electrode by the magnetic force.
Furthermore, as described in Japanese patent publication JP 5-54983, a lamp arrangement is disclosed in which in a lamp, such as a high voltage mercury lamp or the like, a plurality of auxiliary electrodes (outside electrodes) are provided which are situated a few millimeters from one another. However, in this conventional light source device, the emission of a powerful line noise and the formation of an insulation breakdown in an unintended area was not considered at all.
The object of the invention is to eliminate the disadvantages described above, which can be summarized as:
an undesirable increase in the size or weight of the starter should occurs when attempting to avoid heat loss in the windings;
an undesirably large noise forms with conventional discharge lamps;
a greater energy than necessary must be delivered as a result of capacitive coupling, in the vicinity of the starter, between the feed lines and the lead; and
an increased possibility exists for the formation of an insulation breakdown in an unintended area which reduces the reliability of the device.
In a first embodiment of the invention, a light source device is described in which the following components are connected to one another:
a discharge lamp (Ld) including a pair of opposed electrodes (E1, E2) for the main arc discharge and in which an auxiliary electrode (Et) is provided so that the auxiliary electrode does not come into contact with the discharge space (Sd) for the main discharge;
a feed circuit (Bx) for supplying the discharge current to the electrodes (E1, E2) for the main discharge; and
a starter circuit which produces a high voltage between the one of the electrodes (E1, E2) forming the main discharge and the auxiliary electrode (Et),
The object of the invention is achieved by this embodiment in that the high voltage generating part (Ub) of the starter circuit, which includes at least the high voltage transformer (Te), is separated from the feed circuit part (By) such that the lamp (Ld) and the high voltage generating part (Ub) are formed as an integral unit (Ly).
In another embodiment of the invention, a connector for electrical connection of the feed circuit part (By) to the unit (Ly) has the additional function of a holding means for the high voltage generating part (Ub).